Electrical inductance apparatus



y 4, 1963 G. M. STEIN 3,090,022

ELECTRICAL. INDUCTIVE APPARATUS ATTORNEY iliim/ul A May 14, 1963 G. M. STEIN 3,090,022

ELECTRICAL INDUCTIVE APPARATUS Filed April 15, 1960 4 Sheets-Sheet 3 United States Patent 3,tl9t),tl22 ELECTRECAL lINDUQTANfiE APPARATUS Gerhard M. Stein, Sharon, 9a., assiguor to Westinghouse Electric Corporation, East Pittsburgh, Pa, :1 corporation of Pennsylvania Filed Apr. 13, 19st), Ser. No. 21,928 3.9 Claims. (Cl. 336-'7o) This invention relates to electrical inductive apparatus, such as transformers, and more particularly to the windings for such apparatus.

In the windings of certain types of electrical inductive apparatus, such as transformers or reactors, that are connected to transmission lines or electrical power systems, the voltage between the terminals or ends of a winding of such apparatus varies in a substantially uniform manner from one end of the winding to the other during normal frequency and voltage conditions of the system. During certain abnormal operating conditions of the system, however, such as may result from lightning strokes on the transmission system, a high voltage surge or impulse voltage may be impressed on the connected winding of the apparatus to cause a non-uniform distribution of the surge or impulse voltage across said winding and unequal voltage stresses throughout said winding.

In the past, various methods have been employed to protect electrical inductive apparatus, such as transformers, against surge or impulse voltages of the above type. One of the latter methods is to provide large amounts of insulating material between the different sections or portions of the winding which is suflicient to withstand the greatest of the unequal voltage stresses resultin from surge or impulse voltages. The latter method has several important disadvantages since it results in a less compact winding structure and adversely affects the space factor of the winding. Another method which has been employed in the past is to lessen the voltage stresses between the different portions of the winding that are caused by the concentration of surge or impulse voltages by increasing the effective through or series capacitance of an inductive winding.

Heretofore, the eiiective through or series capacitances of an inductive winding have been increased by employing various winding arrangements. Each of the latter winding arrangements has certain limitations with respect to the voltage stresses which result when a surge or impulse voltage is impressed on the winding due to both the initial distribution and subsequent voltage oscillations and with respect to the manner in which interconnections are made between the diilerent portions or sections in said winding arrangements. it is therefore desirable to provide improved winding arrangements of the latter type which will overcome the latter limitations and provide other advantages.

It is an object of this invention to provide a new and improved Winding arrangement for electrical inductive apparatus to improve the distribution of surge or impulse voltages throughout the winding.

Another object of the invention is to provide a winding including a plurality of pancake type or disc type coils in which the interconnections between the different coils are facilitated.

Other advantages of the invention will in part, be obvious and will, in part, appear hereinafter.

The invention accordingly comprises the features or" construction, combination of elements and arrangement of parts which will be exemplified in the construction hereinafter set forth and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a partial sectional elevation of the core and windings of a transformer embodying the teachings of the invention;

FIGS. 2 and 3 are diagrams illustrating the arrangement of the connections at the outside and at the inside, respective, of one of the windings shown in FIG. 1;

FEGS. 4 and 5 are equivalent diagrams illustrating the c-apacitances obtained in one of the windings shown in FIG. 1;

FIG. 6 is a diagram illustrating the interconnections between the different portions or sections of one of the windings shown in FIG. 1;

F168. 7 and 8 are diagrammatic views illustrating a second winding arrangement embodying the teachings of the invention;

l6. 9 is a diagram illustrating a modification of the winding arrangement shown in FIGS. 7 and 8;

FIGS. 10 and 11 are diagrammatic views illustrating a third winding arrangement embodying the teachings of the invention;

FIG. 12 is a diagram illustrating a modification of the winding arrangement shown in FlGS. l0 and 11; and

FIGS. 13 and 14 are diagrammatic views illustrating a fourth winding arrangement embodying the teachings of the invention.

Referring to PEG. 1, there is illustrated a portion of a transformer core and coil assembly 2%) having a winding core leg 32 of ma netic material about which is positioned, in a well-known manner, a primary or high voltage winding at? and a secondary or low voltage winding Ell, which may be of any suitable conventional type and which may include a plurality of conductor turns 36. In this instance, the windings 3t and 4d are disposed in substantially concentric relationship with respect to one another and are insulated from each other and from the core leg 32 by the insulating material 3 As illustrated, the primary winding 46} comprises a plurality of pancake type or disc type coils or annular winding sections 4-2, 44, 46 and 48, which are spaced axially apart from another in a stacked arrangement and which are connected in series circuit relationship with one another. The upper end of the winding 48 is connected to a primary terminal conductor 81 which, in turn, would normally be connected to one of the phases or lines of a transmission system or electrical power system (not shown). The lower end of the winding at the winding section of coil 4-? is connected to the conductor $3 which would connect the coil to an additional plurality of coils, as required in a particular application and as indicated in dotted outline in FIG. 1.

Each of the coil or winding sections 42, 44, 46 and 43 comprises a plurality of turns of at least first and second conductors or conductor strands spirally wound together about a common central axis AA in the winding leg 32 to form first and second coil sections, respectively, whose turns are interleaved with one another in substantially the same plane. For example, it it is assumed that the turns of each of the coils or winding sections 42 through 48 are wound outwardly from the innermost turn, in the coil or winding section the consecutively wound turns of a first conductor would be indicated at $6, and 54 while the consecutively wound turns of a second conductor would be indicated at 53, 52 and 51, the turns of the respective conductors being interleaved with one another to form first and second coil sections 52A and 425, respectively, indicated diagrammatically in FIG. 6. As is customary, a layer of insulating material 43 is disposed between each of the conductor turns forming the coils or winding sections 52 through 48 of the primary winding 4d. Each of the coils or winding sections 44 through 48 also includes a plurality of turns of first and second conductors arranged in the manner just described in detail for the coil or winding section 42 to form first and second coil sections in each of said coils, as shown diagrammatically in FIG. 6.

The turns of the first and second coil sections which make up each of the coils or winding sections 42 through 48 are connected in series circuit relationship with one another, the innermost turn or end of one of the coil sections of each of said coils being connected to the outermost turn or end of the other of said coil sections of each of said coils by the interconnecting conductors or leads 32, 86, 92 and 96, respectively. For example, the innermost turn or end 53 of the second coil section 42A of the coil or winding section 42 is connected to the outermost turn or end 54 of the first coil section 42B of the coil or winding section 42 by the interconnecting conductor or lead 82, as best shown in FIG. 1. The interconnecting conductors 82, 86, 92 and 96 which are disposed in the spaces or ducts between the respective coils or winding sections may be formed integrally with one of the conductors of the connected coils by bending or twisting a continuous extension of one of the first and second conductors which makes up each of the coils 42 through 48, as best shown in FIGS. 2 and 3, or may be provided as a separate channel conductor. If the former method is employed, only one brazed or welded connection is required to provide each of the interconnecting conductors or members 82, 86, 92 and i6.

It is to be noted that because of the manner in which the first and second coil sections of each of the coils 42 through 48 are interconnected, when current flows through the winding 4t) between the terminal conductor 31 and the conductor 98, the current flows initially into each of the first and second coil sections of each of said coils in adjacent turns of the first and second coil sections of each of said coils to thereby increase the effective through or series capacitance in the winding 40. It is also to be noted that when current flows in the winding 4% between the terminal conductor 81 and the conductor 98, the current flows in the same direction through the first and second coil sections of each of the coils 42 or 48 either instantaneously from the outside to the inside or from the inside to the outside of each of said coils or winding sec tions, to insure that the magnetic fluxes produced by the current flow through the first and second coil sections of each of said coils will be in the same direction.

As mentioned previously, the coils or winding sections 42 through 48 of the winding 4-0 are connected in series circuit relationship with one another by the interconnecting conductors or leads 84, 88 and 94, respectively, as best shown in FIGS. 1 and 6. If it is assumed that each of the coils 42 through 43 are wound outwardly from the innermost turn, the interconnecting conductors E3 and 94 connect the innermost or starting turns of the coils 4?. and 44 and 46 and 48, respectively, while the interconnecting conductor 88 connects the outermost or finishing turns of the coils 44 and 46. In order to avoid a brazed or welded connected in the interconnecting conductors 84, 38 and 94 between the coils 42 through 43, the interconnecting conductors 84, 83 and 94 between the respective coils may be formed integrally with one of the conductors which make up one of the interconnected coils by twisting or bending the latter conductor, as best shown in FIGS. 2 and 3, either at the outside or inside of said coils. It is important to note that the length of each of the interconnecting conductors 84, 3S and 94 is considerably reduced, since each of said interconnecting conductors connects either the inner or starting ends of both of the interconnected coils or the outer or finishing ends of both of the interconnected coils rather than being connected between the inner end of one coil and the outer end of the other adjacent coil. The insulation problems associated with the interconnecting conductors S4, 88 and 9d are also reduced since said interconnecting conductors do not pass through the spaces between the respective coils between the inside and the outside of said coils over the turns of the interconnected coils which would require that the interconnecting conductors be insulated for the voltage difference which would exist between the interconnecting conductor and the adjacent turns of each of the interconnected coils.

It is important to note that because of the manner in which the coils 42 through 48 are interconnected in series circuit relationship when current flows between the terminal conductor 81 and the conductor 98, the current flows in opposite directions through successive coils either spirally outwardly or spirally inwardly but in the same circumferential direction. For example, if it is assumed that current is instantaneously flowing in the winding 40 from the terminal conductor $1 to the conduct-or 98, then current will be fiowing spirally inwardly from the outside to the inside of each of the coils 42 and 46, while current will be fiowing spirally outwardly from the inside to the outside of each of the alternate coils 44 and 48. -In order that the magnetic fiuxes produced by current flow through the respective coils be in the same direction in the magnetic core 32, it is therefore necessary that alternate coils be wound in a direction which is opposite to the direction in which the intervening coils are Wound. For example, if it is assumed that each of the coils 42, through 48 is wound outwardly from the innermost turn, then the coils or winding sections 42 and 46 might be wound in a 'coun' terclockwise direction spirally outward from the innerrnost turn of each of said coils, while the coils 44 and 48 would be wound spirally outward from the innermost turn of each of said coils in a clockwise direction, as viewed from the upper end of the winding 49 along the axis A-A. Because of the manner in which the first and second coil sections of each of the coils 4-2 through 48 are interconnected and because of the manner in which the coils 42 through 48 are interconnected as best shown in FIG. 6, a single current path is formed which extends through the winding 4-6 from the line or terminal conductor 81 from the outside to the inside of the coil 42, from the inside to the outside of the coil 44, from the outside to the inside of the coil 46 and firom the inside to the outside of the coil 48 to the conductor 98. It is to be noted that the turns of the coils 42 through 48 are numbered consecutively to indicate cuurrent fiow through the winding 44 when current is instantaneously flowing from the line conductor 81 to the conductor 8 starting with the outermost turn 51 of the coil 42 and that current, therefore, flows in opposite directions either inwardly or outwardly through the successive interconnecting conductors or return conductors S2, 86, 92 and 96, respectively, in the respective coils.

The manner in which the winding arrangement illustrated in FIGS. 1, 2, 3 and 6 increases the through or series capacitance of the winding as is illustrated more clearly in the equivalent diagrams shown in F168. 4 and 5. As mentioned previously, the increased through or series capacitance of the winding 40 results from the manner in which the turns of the first and second sections in each of the coils 42 through 48 are interleaved with one another, from the manner in which said coil sections of each coil are interconnected and from the manner in which the coils 42 through 48 are interconnected. Referring to the equivalent schematic diagram of the winding 4i shown in FIG. 4, the capacitance between each turn of each of the coils 42 through 48 and each of the adjacent turns is indicated at C3 and it is assumed that the latter capacitance is concentrated between the starting points of the respective turns of each of said coils. The starting points of each of the turns 51 through '74 of the coils 42 through 48 are indicated by the corresponding terminals 51 through 74, respectively, in the equivalent schematic diagram of FIG. 4. it will be seen from FIG. 4 that, if the coils 42 through 48 on the winding 40 were wound in the conventional manner from a single conductor and simply connected in series circuit relationship, then the turn to turn capacitances which are part of the resulting or eitective through or series capacitance of the winding 46 would be approximately equal to (11/20 assuming that the coils 42 through 48, as modified in the conventional manner, had the same number of turns as the coils 4 2 through 4 8 shown in FIGS. 1, 2, 3 and 6 and that the efiective through or series capacitance of a conventional winding of the latter type would vary inversely with the total number of turns in the series connected coils. On the other hand, the winding 4th and its equivalent schematic diagram as shown in FIG. 4 may be redrawn in the equivalent schematic diagram shown in FIG. 5 which takes into account the interleaving of the turns of first and second conductors which make up each of the coils 42 through and the manner in which the coil sections of each of said coils are interconnected with each other and with the coil sections of the other coils which make up the winding 40. The turn to turn capacitances which are part of resulting or eifective through or series capacitance of the winding iii, as shown in FIG. 5, are increased over an equivalent conventional winding in the example shown in FIGS. 4 and 5 from a value approximately equal to Cl/ 20 to a value approximately equal to (31/8, which results in a more uniform distribution of voltage stresses when a surge or impulse voltage is impressed across the winding 40 to thereby decrease the insulation required in the Winding and thereby improves the space factor of said winding to thus reduce the size of said winding.

As compared with certain other conventional winding anrangements of the same general type, it has been found also that the winding arrangement illustrated in FIGS. 1, 2, 3 and 6 results in a reduced or lower turn to turn voltage stress in the coils 42 through 4-8 of the winding 40* when a surge or impulse voltage is impressed across the winding 46) during both the initial distribution and subse quent voltage oscillations. In addition, because of the smaller amount or thickness of insulation required on the conductor turns of the coils 42 through 48 through the winding 40, the turn to turn capacitance C1 is increased and a more compact winding structure results.

Referring to FIGS. 7 and 8 a second winding 1 5-3 embodying the teachings of the invention is illustrated. In general, the winding 14b is similar to the winding 4d except that two parallel current paths are provided in the winding 140 which extend throughout the winding 14d.

In particular, the winding 14% includes :a plurality of pancake type or disc type coils or annular winding sections 142, 144, 146 and 143, similarly to the winding 4%. Each of the coils 142 through 1 13 includes a plurality of turns of at least first and second conductors or conductor strands spirally wound together about a common central axis BB in a magnetic core structure (not shown) to form the first and second coil sections in each of said coils, the first and second coil sections of each of said coils being connected in series cincuit relationship by the interconnecting or return conductors 152, 156, 15%; and 164, respectively. For example, if it is assumed that the turns of each of the coils 142 through 148 are wound =out wardly from the innermost turn, then the consecutively wound turns of the first conductor in the coil 142 are indicated at 115, 114, 113, 112 and 111, while the consecutively wound turns of the second conductor in the coil 142 are indicated at 126, 119, 118, 117 and 11s to iorm the first and second coil sections 142A and 1428, respectively, as indicated diagrammatically in FlG. 8. The turns of the first and second coil sections of each of the coils 142 through 148 are interleaved with one another in substantially the same plane similarly to the coils 42 through 48 of the winding it! previously described.

The coil 142 is connected in series circuit relationship with the coil 148 by the interconnecting conductor 162 between the line or terminal conductor 1% and the conductor 263 to form a first current path through the winding 140.. The interconnecting conductor or member 162 connects the inside end or turn of the coil 14-2 to the in side end or turn of the coil 148. Similarly, the coil 144 is connected in series circuit relationship with the ad jacent coil 146 bythe interconnecting conductor or memher 154 between the line or terminal conductor and the conductor 210. The interconnecting conductor or member 154- connects the inside end or turn of the coil 144 to the inside end or turn of the coil 146, to form a second current path through the winding which in general is in parallel with the first current path just described. The coils M2 and 144 taken together constitute a first pair or group of coils which in general is connected in series circuit relationship with a second pair or group of coils which includes the coils 146 and 148.

When current flows through the winding 140, the current which flows in each of the first and second coil sections of each of the coils 142 through 148 flows in the same circumferential direction which is either spiralling inwardly or spirally outwardly so that the magnetic fluxes produced by the current liow in each of the coil sections of each of the coils 142 through 148 is in the same direction in the associated magnetic core structure (not shown). For example, if current is instantaneously flowing into the coils 142 and 144 from the line conductors 108 and 110, respectively, the current will flow from the outside of each of the coil sections 1421A and 144A, respectively, to the inside of each of the coil sections 142A and 144A, respectively, through the interconnecting conductors 152 and 156, respectively, to the outside of each of the coil sections 142B and 1448, respectively, and then to the inside of each of the coil sections 142B and 1443, respectively, to the interconnecting conductors 162 and .154, respectively. It may also be seen from FIGS. 7 and 8 that current flow through the winding 1% will flow through the coils 142 and 144 in a first direction which is either spirally inwardly or spirally outwardly and which is opposite in the latter respect to the direction of the current flow through the coils 146 and 148. In other words, the current flow to the first group of coils which includes the coils 142 and 144 will be in a direction which is either spirally inwardly or spirally outwardly and which is opposite in the latter respect to the current flow in the second group of coils which includes the coils 146 and 148. In order that the magnetic fluxes produced by the current flow through the first group of coils, which includes the coils 142 and 144, will be in the same direction in the associated magnetic core structure as the magnetic fluxes produced by current flow through the second group of coils, which includes the coils 146 and 143, the first group of coils will be wound in a direction which is opposite to the direction in which the second group of coils wound and the current in both groups of coils will then flow in the same circumferential direction around the associated magnetic core structure. For example, if it is assumed that each of the coils 142 through 14-8 is wound outwardly from the innermost or starting turn, then the coils 142 and 144 might be wound in a direction which is counterclockwise about the common axis B-B, while the second group of coils which includes the coils 14 6 and 143 would be wound outwardly from the innermost or starting turn in a direction which is clockwise about the common axis B-B is viewed from the upper end of the windings 1%, Alternatively, if the turns of each of the coils 142 through 148 are wound in the same circumferential direction around the axis BB, then the turns of each of the coils 142 and 144 might be wound inwardly from the outermost turn, while the turns of each of the coils 14-6 and 143 would be wound outwardly from the innermost turn. It is to be noted that the number of brazed or welded connections between the different coils of the windings 149 can be eliminated by forming the interconnections between the difierent coils in a continuous manner integrally with one of the conductors which make up the different coils. For example, the interconnecting conductors 162 and 154 can be formed integrally with one of the conductors which form one of the associated interconnected coils, while only one brazed or welded connection is required to form the interconnecting conductors 152, 156, 158 and 164 integrally with one of the conductors which make up one of the associated coil sections.

Referring to FIG. 8, it is to be understood that a sec ond winding 240 may be provided in a particular application and connected in series circuit relationship with the first winding 141'} to form an overall winding having as many groups of coils as required. The winding 240 also includes a plurality of coils 242 through 248 which are divided into first and second groups which include the coils 242 and 244 and 246 and 248, respectively. It is to be noted from FIG. 8 that the interconnections between successive groups of coils in the windings 140 and 240 are alternately disposed at the inside and the outside, respectively, of the windings 140 and 240 taken together as a single overall winding. Since two parallel current paths are provided in the windings 140 and 24h, windings of the latter type are particularly useful in applications requiring greater current capacity and the winding arrangement shown in FIGS. 7 and 8 possess the same advantages with respect to the increased series or through capacitances which are provided in said windings and the improved voltage distribution which results when a surge or impulse voltage is impressed across the windings 140 and 249, as the winding 49 previously described in detail. It is to be understood that in certain applications, the number of interconnecting conductors can be reduced in the Winding 1441? by connecting the adjacent ends of the coils in each of the groups and then providing a single interconnecting conductor between groups or the interconnections between successive coils could be connected at a single point. For example, the inner ends or turns of the coils 142 and 144 could be brazed or connected by an interconnecting conductor and the inner ends or turns of the coils 146 and 143 of the second group of coils could be similarly brazed or connected together by an interconnecting conductor with only a single interconnecting conductor disposed between the first and second groups of coils of the winding 140 at the inside ends or" said coils. It is also to be understood that the interconnections 152 and 156 in the coils 14-2 and 144 may be combined in certain applications in a single interconnecting conductor which would be disposed between said coils in the winding 14%.

Referring to FIG. 9, a modification of the winding 140 is indicated by the winding 140' shown in FIG. 9. The winding 14% is similar to the winding Mil, except that the coils of each of the first and second groups which include the coils 142' and 144' and 146' and M8, respectively, are connected in parallel circuit relationship with one another, the first and second groups being then connected in series circuit relationship with one another. In particular, the coils 142 and 144' are connected in parallel circuit relationship with one another between the line or terminal conductor 1&7 and the common interconnecting conductor 195, while the coils 146 and 143' of the second group of coils are connected in parallel circuit relationship with one another between the interconnecting conductor 195 and the conductor 169. The first and second groups of coils in the winding 140' are connected in series circuit relationship with one another by the common interconnecting conductor 105, as shown in FIG. 9. The winding modification in FIG. 9 may have certain advantages in particular applications in order to reduce the number of interconnecting conductors required between successive groups of coils in a winding arrangement and it may improve the voltage distribution as compared to the winding 140 shown in FIGS. 7 and 8.

Referring to FIGS. and 11, a third winding arrangement 340 is illustrated embodying the teachings of the in- Q vention. In general, the winding 340 is similar to the winding Mt) previously described in that it provides two parallel current paths through the winding 340, except that the turns of a third conductor in each of the coils of the winding 340 are interleaved between the two parallel current paths provided through the winding 340.

In particular, the winding 340 comprises a plurality of pancake type or disc type coils or annular winding sections 362, 304, 3G6 and 308 similar to the winding 140. Each of the coils 302 through 398 includes at least first, second and third conductors or conductor strands spirally wound together in substantially the same plane about a common central axis CC in an associated magnetic core structure (not shown) to form first, second and third coil sections in each of said coils. For example, if it is assumed that each of the coils 302 through 308 is wound outwardly from the innermost turn, the consecutively wound turns of the first conductor in the coil 3th. are indicated as 354, 353, 352 and 351, the consecutively wound turns of the second conductor are indicated at 318, 317, 316 and 315 and the consecutively wound turns of the third conductor are indicated at 314, 313, 312 and 31-1 to form the first, second and third coil sections 302A, 32-23 and 3lt2C, respectively, indicated diagrammatically in FIG. 11. The turns of two of the three coil sections each of the coils 382 through 3818 are connected in series circuit relationship with one another by the interconnecting or return conductors 382, 384, 386 and 388, respectively, which each connect the outside end or turn of one of the coil sections to the inside end or turn of one of the other two coil sections in each of said coils. For example, in the coil 392, the interconnecting conductor 382 connects the coil sections 3028 and 392C in series circuit relationship by connecting the outer end or finishing turn of the coil section 30213 at the turn 315 to the inside end or starting turn of the coil section 3%?2C at the turn 314.

The two parallel current paths, which are provided in the windings 340, extend through each of the coils 392 through 3% rather than through alternate pairs or groups of coils as in the winding previously described. In particular, the coils 362 through 3'38 are connected in series circuit relationship with one another by the pairs of interconnecting conductors 392 and 394, 395 and 398, and 3% and 395, respectively, between the line or terminal conductors 363 and 385 and the conductors 307 and 309, respectively, as best shown in FIG. 11. It is to be noted that the additional interleaved turns of the third conductor in each of the coils 362 through 3'88 are alternately connected in one or the other of the two current paths in successive coils by the interconnections of the coil sections of each of said coils and the interconnections between the different coils, as just described, to substantially balance the ampere-turns provided in each of the two parallel current paths in the winding 340.

When current flows through the winding 340, if it is assumed that current flows into the coil 332 at the line conductors 303 and 3%, a first current path will result which extends from the outside of the coil sections 302A of the coil 392 to the inside of the coil section 3fi2A, through the interconnecting conductor 3% to the inside of the coil section 394B of the coil 304, to the outside of the coil section 30413, through the interconnecting conductor 384 to the inside of the coil section 3040, to the outside of the coil section 3M0, through the interconnecting conductor 398 to the outside of the coil section 3tt6A, to the inside of the coil section 306A of the coil 3%, through the interconnecting conductor 3% to the inside of the coil section 30813 of the coil 308, to the outside of the coil section 30813, through the interconnecting conductor 388 to the inside of the coil section 398C, to the outside of the coil section 398C, and finally to the conductor 307. The second parallel current path through the winding 349 will extend from the conductor 365 from the outside to the inside of the coil section 302C of the coil 3%, through the interconnecting conductor 3&2, to the outside of the coil section 30213, to the inside of the coil section 302B through the interconnecting conductor 392. to the inside of the coil section 304A, to the outside of the coil section 3ii'4A, through the interconnecting conductor 3% to the outside of the coil section 3%C of the coil 3%, to the inside of the coil section 3%, through the interconnecting conductor 386 to the outside of the coil section 3%13, to the inside of the coil section 3MB, through the interconnecting conductor 393 to the inside of the coil section 393A of the coil 30% to the outside of the coil section FihSA and finally to the conductor 399. The winding 346 provides certain advantages with respect to the ease of making interconnections over the windings Mil and 141i illustrated in FIGS. 8 and 9.

Referring to FIG. 12, a modification of the winding 34% shown in FIG. 11 is indicated by the winding arrangement 34% which, in general, is similar to the winding 340 except that the winding 340 provides two parallel current paths with the additional interleaved turns of a third conductor disposed on one side of two adjacent conductor turns rather than being disposed intermediate the associated conductor turns in each of the coils.

In particular, the winding 3% similarly includes a plurality of pancake type or disk-type coils or annular winding sections 3% through 3438 which are connected in series circuit relationship with one another to form two parallel current paths through the winding 340' similarly to the winding 3443-. Each of the coils 362 through Sti t includes a plurality of turns of at least first, second and third conductors spirally wound together in substantially the same plane to form first, second and third coil sections, respectively, in each of the coils 392 through 3%. The turns of the third coil section in each of the coils W2 through 308 are alternately connected in series circuit relationship with one of the adjacent first and second coil sections with whose turns the third coil section is interleaved either on the outside or the inside of the associated coil sections in each of said coils. For example, the turns of the third coil section 302C in the coil 362 are connected in series circuit relationship with the turns of the first coil section 3ii2A by the interconnecting conductor 382 which connects the outside or finishing turn or end of the third coil section 3492C with the inside or starting turn or end of the first coil section 3632A While the interconnecting conductors 384, 38-6 and 38% provide similar connections in the coils 304', 3% and 3%, respectively. It is to be noted that the interconnecting conductors between the successive coils 392 through 3% are alternately provided either at the inside or starting turns of the respective coils or at the outside or finish turns of the respective coils as shown in EEG. 12. It is also to be noted that the interconnecting conductors 382', 384', 386' and $38 in the coils 3th? through 3%, respectively, of the winding 3 39' are disposed in the axial spaces between the respective coils similarly to the windings it), 149, 14-4) and 34 0.

Referring to FIGS. 13 and 14, there is illustrated a fourth winding arrangement which is similar to the windings 140 and 340, except that the winding 590 pro vides three parallel current paths through the winding rather than only two current paths as provided in each of the windings 114i) and 340. More specifically, the winding 55%? similarly includes a plurality of pancake type or disk-type coils or annular winding sections 502, 504, 5% and 5%- which are connected in series circuit relationship with one another to provide three parallel current paths through said winding.

In particular, each of the coils 502 through 508 includes at least first, second and third and fourth conductors or conductor strands spirally wound together in substantiaL ly the same plane about a common central axis DD in an associated magnetic core structure (not shown) to provide, first, second, third and fourth coil sections, respectively, in each of said coils. For example, if it is 10 assumed that each of the coils 502 through 508 is wound outwardly from the innermost turn, in the coil 502, the consecutively wound turns of the first conductor are indicated at 57 i, 573, 572 and 571, the consecutively wound turns of a second conductor are indicated at 554, 553, 552 and 551, the consecutively wound turns of a third conductor are indicated at 5'34, 533, 5-32 and 531 and the consecutively wound turns of a fourth conductor are indicated at 514, 513, 512. and 511 to form the first, second, third and fourth coil sections 562A, 50213, 5020 and 5821), respectively, which are indicated diagrammatically in PEG. 14. The turns of the different conductors or coil sections of each of the coils 502 through 568 are continuously interleaved with one another similarly to the winding arrangements previously described to increase the efiective through or series capacitance in the winding 55%. The additional conductor turns of the fourth conductor are consecutively connected in series circuit relationship with the turns of one of the first, second or third coil sections in each of the coils 5% through see, respectively by the interconnecting conductors 592, 594, 596 and 598, respectively. For example, the outside or finishing turn of the fourth coil section SEEZD is connected by the interconnecting conductor 592 in the coil 502 to the inside or starting turn or end of the first coil section 562A of the coil 5&2. More specifically, additional turns of the fourth coil section in the coils Sti t- 506 and 508- are connected in sequence in series circuit relationship with the turns of the second, third and first coil sections, respectively, with the sequence of interconnections being repeated in successive groups of at least three coils in order to balance the ampere-turns in each of the three parallel current paths provided in the winding 5%, whenever current flows through the coils 56 2 through St)? of the winding 596*. The line or terminal conductors of the winding 59% are indicated at Siil, see and 505 and the corresponding conductors at the other end of the winding 5% are indicated at 6&2, sat and 6%, respectively, with the coils 5632 through 5&8 being connected in series circuit relationship between said sets of conductors by the three interconnecting conductors provided between successive coils alternately at the inside and at the outside of the respective coils, as best shown in FIGS. 13 and 14.

Whenever current flows through the winding 590 between the line or terminal conductors 501, 563 and 505 and the corresponding conductors 602, 694 and 606 at the other end of said winding, the current divides into three substantially parallel paths. The winding 590 may be employed in a particular application to obtain greater current capacity in a winding arrangement of the type disclosed. It is to be noted that the interconnections between the successive coils of the winding 5% may be made without welded or brazed connections by continuously winding the conductors which connect the successive adjacent coils and that the interconnection, which provides interleaving, hetween the conductors or coil sections of the same coil may be made with only one brazed or welded connection by forming the interconnected conductor integrally with one of the conductors of the coil in a continuous manner by twisting or bending as previously described in connection with the winding 40. It is to be noted that in the windings 349 and 590, the interconnections between the successive coils of said windings require transposing the conductors of at least one of the interconnected coils. It is to be noted also that in the winding 5%, the current flows in opposite directions through the successive coils either spirally inwardly or spirally outwardly and, therefore, the alternate coils of the winding 59% would have to be wound in an efi'ective winding direction which is opposite to the direction in which the intervening coils are wound in order that current flow through successive coils of the winding 5'96 in the same circumferential direction. In other words, if it is assumed that the coils 502 through 508 are all wound outwardly rom the innermost turn, then the coils 502 and 506 might be wound in a counterclockwise direction from the innermost turn, while the coils G4 and 598 would be wound in a clockwise direction from the innermost turn as viewed from the upper end of the winding 5% along the common axis DD. It is also to be understood that the winding 590 may be modified similarly to the winding 34% shown in FIG. 11 in order to dispose the additional turns of the fourth conductor or coil section of each of the coils 502 through 5% intermediate the turns of the first, second or third conductors or coil sections in each of said coils in order to obtain difierent through or series capacitances in the winding 590. Similarly to the winding 340, the interconnections between the successive coils of the winding 590 are alternately made at the inside and at the outside of the respective coils, as indicated in FIGS. 13 and 14.

In summary, it is to be noted that each of the windings 140, 140', 340, 340, and 596 has the advantage that the interconnections between the difierent coils are reduced in length by connecting either the inner or starting ends or" the respective coils or the outer or finish ends of the respective coils rather than having the interconnections pass over the turns of the interconnected coils in the spaces between the respective coils which creates the insulation problems previously mentioned. It is obvious also that the teachings of the invention may be extended to winding arrangements in which a number of parallel current paths are provided greater than those disclosed by extending the principles of the invention. As previously mentioned, it is to be understood that where coils or groups of coils are to be wound in circumferentially opposite directions, either clockwise or counterclockwise, about a common axis in the different winding arrangements disclosed assuming that the coils are to be wound outwardly from the innermost turn, the same results could be obtained by winding the turns of all of the coils in the different winding arrangements in the same circumferential direction, which may be either clockwise or counterclockwise, but with alternate coils or groups of coils being wound either spirally inwardly from the outermost turn or spirally outwardly from the innermost turn in order to obtain the same direction of magnetic fiux produced by the current flow in the successive coils or groups of coils of the different winding arrangements in the associated magnetic core structures.

The apparatus embodying the teachings of this invention has several advantages. For example, a greater series or through capacitance is provided in the difierent winding arrangements disclosed in order to reduce the voltage stresses in the different portions of the Winding arrangements when a surge or impulse voltage is impressed on the winding. The excessive voltage stresses which might otherwise result in a conventional winding arrangement would require either excessive insulation around the different portions or" the winding or a winding failure might result because of excessive voltage stresses. The latter voltage stresses might result during either the initial distribution or subsequent voltage oscillations when a surge or impulse voltage is present in the transmission system or electrical power system to which a conventional winding is connected. By reducing the voltage stresses between adjacent turns in the coils or winding sections of the winding arrangement disclosed, a more compact winding structure results which also permits a reduction in the physical size or amount of magnetic material required in the associated magnetic core structure. The above advantages are particularly important in limiting the physical size and Weight of electrical inductive appa ratus, such as transformers Whose voltage and power ratings are continually increasing.

Since numerous changes may be made in the above described apparatus and diiTerent embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all the matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. A winding for an electrical inductive apparatus comprising a plurality of coils arranged in a stack, each of said coils including a plurality of turns of at least first and second conductors spirally wound together, the inner end of said first conductor being connected to the outer end of said second conductor in each coil, the turns of alternate coils being wound in a direction which is opposite to that or" the turns of the adjacent coils, the inner end of the second conductor in each coil being connected to the inner end of the second conductor in one of the adjacent coils and the outer end of the first conductor in each coil being connected to the outer end of the first conductor in one of the adjacent coils to connect said coils in series circuit relation to form a single current path through said Winding.

2. A winding for an electrical inductive apparatus comprising a plurality of disc type coils arranged in a stack, each of said coils including a plurality of turns of at least first and second conductors spirally wound together, the inner end of said first conductor being connected to the outer end of said second conductor in each coil, the turns of alternate coils being wound in a direction which is opposite to that of the turns of the adjacent coils, the inner end of the second conductor in each coil being connected to the inner end of the second conductor in one of the adjacent coils and the outer end of the first conductor in each coil being connected to the outer end of the first conductor in one of the adjacent coils to connect said coils in series circuit relation to form a single current path through said winding, the current which flows in alternate groups of coils being in a direction which is either spirally inwardly or spirally outwardly and which is opposite in the latter respect to that of the current in the intervening groups of coils.

3. A winding for an electrical inductive apparatus comprising a plurality of coils arranged in a stack, each of said coils including a plurality of turns of at least first and second conductors spirally wound together, the inner end of said first conductor being connected to the outer end of said second conductor in each coil, the turns of the first and second conductors in each coil being continuously interleaved with one another, the turns of alternate coils being wound in a direction which is opposite to that of the turns of the adjacent coils, the inner end of the second conductor in each coil being connected to the inner end of the second conductor in one of the adjacent coils and the outer end of the first conductor in each coil being connected to the outer end of the first conductor in one of the adjacent coils to connect said coils in series circuit relation to form a single current path through said plurality of coils.

4. An electrical inductive apparatus comprising a magnetic core, a winding disposed on said core, said winding comprising a plurality of disc-type coils arranged in a stack, each of said coils including a plurality of turns of at least first and second conductor strands spirally wound together about a portion of said core, the inner end of said first conductor strand being connected to the outer end of said second conductor strand to connect the conductor strands of each coil in series circuit relation, the turns of alternate pairs of said coils being wound in a direction which is opposite to that of the adjacent pairs of coils, each coil of each pair of coils being connected in series circuit relation with one of the coils in each adjacent pair of coils at the inner and outer ends thereof to form at least two parallel current paths through said winding.

5. An electrical inductive apparatus comprising a magnetic core, a winding disposed on said core, said winding comprising a plurality of disc-type coils arranged in a stack, each of said coils including a plurality of turns of at least first and second conductor strands spirally wound together about a portion of said core, the inner end of said first conductor strand being connected to the outer end of said second conductor strand to connect the conductor strands of each coil in series circuit relation, the turns of alternate pairs of said coils being wound in a direction which is opposite to that of the adjacent pairs of coils, the inner end of one conductor strand of each coil being connected to the inner end of one of the conductor strands of one coil of one adjacent pair of coils and the outer end of the other conductor strand of each coil being connected to the outer end of one of the conductor strands of one coil of the other adjacent pair of coils to form at least two parallel current paths through said winding.

6. An electrical inductive apparatus comprising a magnetic core, a winding disposed on said core, said Winding comprising a plurality of disc-type coils arranged in a stack, each of said coils including a plurality of turns of at least first and second conductor strands spirally wound together about a portion of said core, the inner end of said first conductor strand being connected to the outer end of said second conductor strand to conect the conductor strands of each coil in series circuit relation, the turns of alternate pairs of said coils being wound in a direction which is opposite to that of the adjacent pairs of coils, each coil of each pair of coils being connected in series circuit relation with one of the coils in each adjacent pair of coils at the inner and outer ends thereof to form at least two parallel current paths through said winding, the current which flows in each alternate pair or" said coils being in a direction which is either spirally inwardly or spirally outwardly and which is opposite in the latter respect to that of the current in the intervening pairs of coils.

7. An electrical inductive apparatus comprising a magnetic core, a Winding disposed on said core, said winding comprising a plurality of disc-type coils arranged in a stack, each of said coils including a plurality of turns of at least first and second conductor strands spirally wound together about a portion of said core, the turns of the first and second conductor strands of each coil being con tinuously interleaved with one another, the inner end of said first conductor strand being connected to the outer end of said second conductor strand to connect the conductor strands of each coil in series circuit relation, the turns of alternate pairs of said coils being wound in a direction which is opposite to that of the adjacent pairs of coils, each coil of each pair of coils being connected in series circuit relation with one of the coils in each adjacent pair of coils at the inner and outer ends thereof to form at least two parallel current paths through said Winding.

8. An electrical inductive apparatus comprising a magnetic core, a winding disposed on said core, said winding comprising a plurality of pancake type coils, each of said coils including a plurality of turns of at least first and second conductors spirally wound together about a portion of said core, the inner end of said first conductor being connected to the outer end of said second conductor to connect the conductors of each cell in series circuit relation, the turns of alternate pairs of said coils being wound in a direction which is opposite to that of the intervening pairs of coils, the free inner ends of the second conductors of each pair of coils being connected to those of the second conductors in one of the adjacent pairs of coils, the free outer ends of the first conductors of each pair of coils being connected to those of the first conductors in the otier adjacent pair of coils, the conductors of each coil of each pair of coils being connected in parallel circuit relation with the conductors of the other coil of said pair, each of said pairs of coils being connected in series circuit relation with the adjacent pairs of coils.

9. An electrical inductive apparatus comprising a magnetic core, a winding disposed on said core, said winding comprising a plurality of pancake type coils, each of said cells including a plurality of turns of at least first and second conductors spirally wound together about a portion of said core, the inner end of said first conductor being connected to the outer end of said second conductor to connect the conductors of each coil in series circuit relation, the turns of alternate pairs of said coils being wound in a direction which is opposite to that of the adjacent pairs of coils, the conductors of each coil of each pair of coils being connected in parallel circuit relation with the conductors of the other coil of said pair, each of said pairs of coils being connected in series circuit relation with the adjacent pairs of coils, the current which flows in each alternate pair of coils being in a direction which is either spirally inwardly or spirally outwardly and which is opposite in the latter respect to that of the current which flows in the intervening pairs of coils.

10. An electrical inductive apparatus comprising a magnetic core, a winding disposed on said core, said winding comprising a plurality of disc-type coils arranged in a stack, each of said coils including a plurality of turns of at least three conductors spirally Wound together about a portion of said core, the turns of alternate coils being wound in a direction opposite to that of the intermedaite coils, the inner and outer ends of the intermediate conductors of successive coils being alternately connected to the opposite end of one of the other conductors of the same coil to connect the turns of the intermediate conductor in series with the turns of the other conductor in the same coil, each of the two free inner ends of the conductors in each coil being connected to one of the two free inner ends of the conductors of one of the adjacent coils and each of the two free outer ends of the conductors in each coil being connected to one of the free outer ends of the conductors of one of the adjacent coils to connect said coils in series and form at least two parallel current paths through said winding.

ll. An electrical inductive apparatus comprising a magnetic core, a winding disposed on said core, said winding comprising a plurality of disc-type coils arranged in a stack, each of said coils including a plurality of turns of at least three conductors spirally wound together about a portion of said core, the turns of alternate coils being wound in a direction opposite to that of the intermediate coils the inner and outer ends of the intermediate conductors of successive coils being alternately connected to the opposite end of one of the other conductors of the same coil to connect the turns of the intermediate condoctor in series with the turns of the other conductor in the same coil, each of the two free inner ends of the conductors in each coil being connected to one of the two free inner ends of the conductors of one of the adjacent coils and each of the two free outer ends of the conductors in each coil being connected to one of the free outer ends of the conductors of one of the adjacent coils to connect said coils in series and forth at least two parallel current paths through said winding, the current which flows in alternate coils being in a direction which is either spirally inwardly or spirally outwardly and which is opposite in the latter respect to that of the current which flows in the intervening coils.

12. An electrical inductive apparatus comprising a magnetic core, a winding disposed on said core, said winding comprising a plurality of pancake type coils, each of said coils including a plurality of turns of at least first, second and third conductor strands, said strands of each coil being spirally wound together about a portion of said core, the turns of successive coils being alternately wound in effectively opposite directions, the turns of the third conductor in successive coils being alternately connected at one end thereof in series with the turns of the first or second conductors at the opposite end thereof to form two parallel current paths in each coil, the remaining free inner ends of at least two conductors of spasms each coil being connected respectively to the free inner ends of two conductors in one adjacent coil and the remaining free outer ends of at least two dififerent conductors being connected respectively to the free outer ends of two conductors in the other adjacent coil to form two parallel current paths through said winding.

13. An electrical inductive apparatus comprising a magnetic core, a winding disposed on said core, said winding comprising a plurality of pancake type coils, each of said coils including a plurality of turns of at least first, second and third conductor strands, said strands of each coil being spirally Wound together about a portion of said core, the turns of the first, second and third conductor strands of each coil lying in substantially the same plane and being continuously interleaved with one another, the turns of successive coils being wound in opposite directions, the turns of the third conductor in each of the successive coils being alternately connected at one end thereof in series with the turns of the first one end thereof in series with the turns of the first or second conductors of the same coil at the opposite end thereof to form two parallel current paths in each coil, each of the two f ee inner ends of at least two conductors of each coil being connected respectively to one of the two free inner ends of two conductors in one adjacent coil and each of the two free outer ends of at least two conductors of each coil being connected to one of the two free outer ends of two conductors in the other adjacent coil to form two parallel current paths through said winding.

14. An electrical inductive apparatus comprising a magnetic core, a winding disposed on said core, said winding comprising a plurality of disc type coils, each of said coils including a plurality of turns of at least first, second, third and fourth conductors spirally wound together in the same direction about a portion of said core, the turns of successive coils being alternately wound in opposite directions, the turns of the fourth conductor in successive coils being successively connected at one end thereof in series with the turns of the first, second and third conductors at the opposite end thereof to form three parallel current paths through each coil, each of the three free inner ends of at least three conductors in each coil being connected respectively to one of the three free inner ends of three conductors in one adjacent coil and each of the three free outer ends of at least three conductors of each coil being connected to one of the three free outer ends of three conductors in the other adjacent coil to form three parallel current paths through said winding.

15. An electrical inductive apparatus comprising a magnetic core, a winding disposed on said core, said winding comprising a plurality of disc-type coils, each of said coils including a plurality of turns of at least first, second, third and fourth conductors spirally wound together in the same direction about a portion of said core, the turns of successive coils being wound in opposite directions outwardly from the innermost turn, the turns of the fourth conductor in each of the successive coils being successively connected at one end thereof in series with the turns of the first, second and third conductors of the same coil at the opposite end thereof to form three parallel current paths through each coil, each of the three free inner ends of at least three conductors in each coil being connected respectively to one of the three free inner ends of three conductors in one adjacent coil and each of the three free outer ends of at least three conductors of each coil being connected to one of the three free outer ends of three conductors in the other adjacent coil to form three parallel current paths through said winding, the current which flows in alternate coils being in a direction which is either spirally inwardly or spirally outwardly and which is opposite in the latter respect to that of the current which flows in the intervening coils.

16. A winding for an electrical inductive apparatus comprising a plurality of coils arranged in a stack, each of said coils including a plurality of turns of at least first and second conductors spirally wound together, the inner end of said first conductor being connected to the outer end of said second conductor in each coil, the turns of alternate coils being wound spirally outwardly from the innermost turn and the turns of the intervening coils being wound spirally inwardly from the outermost turn, the turns of all coils being wound in the same circumferential direction, the inner end of the second conductor in each coil being connected to the inner end of the second conductor in one of the adjacent coils and the outer end of the first conductor in each coil being connected to the outer end of the first conductor in one of the adjacent coils to connect said coils in series circuit relation to form a single current path through said winding.

17. An electrical inductive apparatus comprising a magnetic core, a winding disposed on said core, said winding comprising a plurality of disc-type coils arranged in a stack, each of said coils including a plurality of turns of at least first and second conductor strands spirally wound together about a portion of said core, the inner end of said first conductor strand being connected to the outer end of said second conductor strand to connect the conductor strands of each coil in series circuit relation, the turns of alternate pairs of coils being spirally wound about a common axis in a direction which is circumferentially opposite to that of the intervening pairs of coils with respect to said axis, the turns of all of said coils being spirally wound outwardly from the innermost turn, the inner end of one conductor strand of each coil being connected to the inner end of one of the conductor strands of one coil of one adjacent pair of coils and the outer end of the other conductor strand of each coil being connected to the outer end of one of the conductor strands of one coil of the other adjacent pair of coils to form at least two parallel current paths through said winding.

18. An electrical inductive apparatus comprising a magnetic core, a winding disposed on said core, said winding comprising a plurality of disc-type coils arranged in a stack, each of said coils including a plurality of turns of at least three conductors spirally wound together about a portion of said core, the turns of alternate coils being wound spirally outwardly from the innermost turn and the turns of the intervening coils being wound spirally inwardly from the outermost turn, the turns of all coils being wound in the same circumferential direction, the inner and outer ends of the intermediate conductors of successive coils being alternately connected to the opposite end of one of the other conductors of the same coil to connect the turns of the intermediate conductor in series with the turns of the other conductor in the same coil, each of the two free inner ends of the conductors in each coil being connected to one of the two free inner ends of the conductors of one of the adjacent coils and each of the two free outer ends of the conductors in each coil being connected to one of the free outer ends of the conductors of one of the adjacent coils to connect said coils in series and form at least two parallel current paths through said winding.

19. An electrical inductive apparatus comprising a magnetic core, a winding disposed on said core, said winding comprising a plurality of disc-type coils, each of said coils including a plurality of turns of at least first, second, third and fourth conductors spirally Wound together in the same direction about a portion of said core, the turns of alternate coils being spirally wound about a common axis in a direction which is circumferentially opposite to that of the intervening coils with respect to said axis, the turns of all of said coils being wound outwardly from the innermost turn, the turns of the fourth conductor in each of the successive coils being successively connected at one end 17 thereof in series with the turns of the first, second and third conductors of the same coil at the opposite end thereof to form three parallel current paths through each coil, each of the three free inner ends of at least three conductors in each coil being connected respectively to one of the three free inner ends of three conductors in one adjacent coil and each of the three free outer ends of at least three conductors of each coil being connected to one of the three free outer ends of three conductors in the other adjacent coil to form three parallel current paths through said winding, the current which flows in alternate coils being in a direction which is either spirally inwardly or spirally outwardly and which is opposite in the latter respect to that of the current which flows in the inter-' vening coils.

References {Iited in the file of this patent UNITED STATES PATENTS 2,862,195 Kury Nov. 25, 1958 FOREIGN PATENTS 1,147,282 France June 3, 1957 516,823 Italy Feb. 24, 1955 314,113 Switzerland July 14, 1956 745,390 Great Britain Feb. 22, 1956 

16. A WINDING FOR AN ELECTRICAL INDUCTIVE APPARATUS COMPRISING A PLURALITY OF COILS ARRANGED IN A STACK, EACH OF SAID COILS INCLUDING A PLURALITY OF TURNS OF A LEAST FIRST AND SECOND CONDUCTORS SPIRALLY WOUND TOGETHER, THE INNER END OF SAID FIRST CONDUCTOR BEING CONNECTED TO THE OUTER END OF SAID SECOND CONDUCTOR IN EACH COIL, THE TURNS OF ALTERNATE COILS BEING WOUND SPIRALLY OUTWARDLY FROM THE INNERMOST TURN AND THE TURNS OF THE INTERVENING COILS BEING WOUND SPIRALLY INWARDLY FROM THE OUTERMOST TURN, THE TURNS OF ALL COILS BEING WOUND IN THE SAME CIRCUMFERENTIAL DIRECTION, THE INNER END OF THE SECOND CONDUCTOR IN EACH COIL BEING CONNECTED TO THE INNER OF THE SECOND CONDUCTOR IN ONE OF THE ADJACENT COILS AND THE OUTER END OF THE FIRST CONDUCTOR IN EACH COIL BEING CONNECTED TO THE OUTER END OF THE FIRST CONDUCTOR IN ONE OF THE ADJACENT COILS TO CONNECT SAID COILS IN SERIES CIRCUIT RELATION TO FORM A SINGLE CURRENT PATH THROUGH SAID WINDING. 